While not knowing the particulars behind the deal, I can confidently say that Showtime paid a boatload of money to Floyd Mayweather.

He had a very good deal with HBO Sports, but Golden Boy (who helps Floyd with his promotions) and Al Haymon (Mayweather’s adviser) have a great relationship with Showtime. Here is how Leonard Ellerbe describe the negotiations.

Ellerbe on @FloydMayweather's deal:'HBO, they made a great offer the but Showtime PPV/CBS offer was substatnitially greater in every facet.'

Undefeated eight-time world champion Floyd “Money” Mayweather, boxing’s pound-for-pound king and the highest paid athlete in the world (Forbes, 2012), has entered into a groundbreaking pay-per-view deal with Showtime Networks Inc. and its parent company, CBS Corporation. Under the new deal, SHOWTIME PPV® will collaborate with CBS Corporation to comprehensively promote Mayweather’s events on the CBS Television Network and via the corporation’s expansive media platforms.

The deal-a unique revenue-sharing arrangement between SHOWTIME PPV and Mayweather-will enable him to fight up to six times over a period of 30 months, with the first mega-event taking place on May 4, 2013, when Mayweather will fight Robert “The Ghost” Guerrero. More details of this upcoming event will be announced shortly.